<template>
  <div class="music-list">
    <div class="back" @click='back'>
      <i class="icon-back"></i>
    </div>

    <h1 class="title" v-html='title'></h1>
    <div class="bg-image" :style='bgStyle' ref='bgImage'>
      <div class="play-wrapper">
        <div class="play" v-show='songs.length>0' ref='playBtn' @click='random'>
          <i class="icon-play"></i>
          <span class="text">随机播放全部</span>
        </div>
      </div>
      <div class="filter" ref='filter'></div>
    </div>
    
    <!-- 信息列表上下滑动时遮罩层 -->
    <div class="bg-layer" ref='layer'>
      
    </div>
    <scroll @scroll='scroll' :data='songs' class='list' ref='list' :probe-type='probeType' :listen-scroll='lisenScroll'>
      <div class="song-list-wrapper">
        <song-list :rank='rank' @select='selectItem' :songs='songs'></song-list>
      </div>

      <div class="loading-wrapper" v-show='!songs.length'>
        <loading></loading>
      </div>
    </scroll>
  </div>
</template>

<script type="text/ecmascript-6">
  import Scroll from 'base/scroll/scroll'
  import SongList from 'base/song-list/song-list'
  import {prefixStyle} from 'common/js/dom'
  import Loading from 'base/loading/loading'
  // vuex提供的调用actions方法的语法糖
  import {mapActions} from 'vuex'

  import {playlistMixin} from 'common/js/mixin'

  const TOP_HEIGHT = 40;
  const transform = prefixStyle('transform')
  const backdrop = prefixStyle('backdrop-filter')

  export default {
    // 组件同名方法会覆盖mixin方法
    mixins: [playlistMixin],
    props:{
      bgImage: {
        type: String,
        default: ''
      },
      songs: {
        type: Array,
        default: []
      },
      title: {
        type: String,
        default: ''
      },
      rank: {
        type: Boolean,
        default: false
      }
    },
    data(){
      return {
        scrollY :0
      }
    },
    created() {
      // 传递给scroll组件，监听滚动时的滚动事件，将其返回并进行操作
      this.probeType = 3
      this.lisenScroll = true
    },
    methods:{
      handlePlaylist(playlist) {
        const bottom = playlist.length > 0 ? '60px' : ''
        this.$refs.list.$el.style.bottom = bottom;
        this.$refs.list.refresh();
      },
      //监听滚动列表的滚动事件
      scroll(pos){
        this.scrollY = pos.y;
      },
      //返回歌手列表页
      back(){
        this.$router.back();
      },
      // 选中播放歌曲
      selectItem(item, index) {
        this.selectPlay({
          list: this.songs,
          index: index
        })
      },
      // 随机播放全瓿
      random() {
        this.randomPlay({
          list: this.songs
        })
      },
      // 使用mapActions代理选中歌曲操作
      ...mapActions([
        'selectPlay',
        'randomPlay'
      ])
    },
    watch: {
      scrollY(newY) {
        // 取图片的高度值和滚动位置的最大值，为layer最大滚动高度
        let translateY = Math.max(this.minTranslateY,newY) + TOP_HEIGHT;
        let zIndex = 0;
        let scale = 1;//图片放大缩小
        let blur = 0;//背景模糊效果
        this.$refs.layer.style[transform] = `translate3D(0,${translateY}px,0)`
        // 背景图根据滑动情况实现放大缩小
        const percent = Math.abs(newY/this.imageHeight);
        if(newY > 0){
          scale = 1 + percent; 
          zIndex = 10;
        }else{
          blur = Math.min(20*percent,20);
        }
        this.$refs.filter.style[backdrop] = `blur({$blur}px)`

        // 当滚动值超过最大滚动值时，改变背景图的显示方式，让背景的层级盖住滚动列表
        if(newY < this.minTranslateY){
          this.$refs.bgImage.style.paddingTop = 0;
          this.$refs.bgImage.style.height = TOP_HEIGHT + 'px';
          zIndex = 10;
          this.$refs.playBtn.style.display = 'none'
        }else{
          this.$refs.bgImage.style.paddingTop = '70%';
          this.$refs.bgImage.style.height = 0;
          this.$refs.playBtn.style.display = ''
        }
        this.$refs.bgImage.style.zIndex = zIndex;
        this.$refs.bgImage.style[transform] = `scale(${scale})`
      }
    },
    computed:{
      bgStyle(){
        return `background-image:url(${this.bgImage})`
      }
    },
    mounted() {
      this.imageHeight = this.$refs.bgImage.clientHeight;
      this.minTranslateY = -this.imageHeight;
      // 列表加载完成后，动态计算头部图片高度并手动改变列表容器的位置
      this.$refs.list.$el.style.top = `${this.imageHeight}px`
    },
    components: {
      Scroll, SongList, Loading
    }
  }
</script>

<style lang='stylus' rel='stylesheet/stylus'>
  @import "~common/stylus/variable";
  @import "~common/stylus/mixin";

  .music-list
    position: fixed
    z-index: 100
    top: 0
    left: 0
    bottom: 0
    right: 0
    background: $color-background
    .back
      position absolute
      top: 0
      left: 6px
      z-index: 50
      .icon-back
        display: block
        padding: 10px
        font-size: $font-size-large-x
        color: $color-theme
    .title
      position: absolute
      top: 0
      left: 10%
      z-index: 40
      width: 80%
      no-wrap()
      text-align: center
      line-height: 40px
      font-size: $font-size-large
      color: $color-text
    .bg-image
      position: relative
      width: 100%
      height: 0
      padding-top: 70%
      transform-origin: top
      background-size: cover
      .play-wrapper
        position: absolute
        bottom: 20px
        z-index: 50
        width: 100%
        .play
          box-sizing: border-box
          width: 135px
          padding: 7px 0
          margin: 0 auto
          text-align: center
          border: 1px solid $color-theme
          color: $color-theme
          border-radius: 100px
          font-size: 0
          .icon-play
            display: inline-block
            vertical-align: middle
            margin-right: 6px
            font-size: $font-size-medium-x
          .text
            display: inline-block
            vertical-align: middle
            font-size: $font-size-small
      .filter
        position: absolute
        top: 0
        left: 0
        width: 100%
        height: 100%
        background: rgba(7, 17, 27, 0.4)
    .bg-layer
      position: relative
      height: 100%
      background: $color-background
    .list
      position: fixed
      top: 0
      bottom: 0
      width: 100%
      background: $color-background
      .song-list-wrapper
        padding: 20px 30px
      .loading-container
        position: absolute
        width: 100%
        top: 50%
        transform: translateY(-50%)
</style>